1. I think tone is usually the easiest starting point. Ask yourself - what are the tones of the two articles? Are they similar? Different? (usually they'll give you two articles with quite different tones) Then ask - what effect does the difference have? In terms of how I'm made to feel, made to think about the issue?
2. Look at the different kinds of techniques used by the two articles. Is there overlap? If so, are the techniques used the same way, or differently? (try to emphasise the differences) OR is there a bit difference in terms of the kinds of techniques used? (eg. techniques that appeal to rationality, like statistics and appeals to authority VS techniques that are more emotionally-centered, like imagery and inclusive language) If so, discuss that difference and point it out.
3. Usually you don't have to make a big deal about comparison. My advice would be to analyse the first article as normal, and then make constant comparisons between the first and the second whilst you're analysing the second. At the end of the day, being comparative is pretty much just another box to tick and make sure you're doing adequately, as opposed to the focus of the task.